During the past decade there was an enormous increase in research on sphingolipids due to discoveries that implicated members of this group in signal transduction processes [reviewed in Levade et al., Biochim. Biophys. Acta 1438, 1-17, (1999); Mathias et al., Biochem. J. 335, 465-80, (1998); Perry et al., Biochim. Biophys. Acta 1436, 233-43, (1998); Riboni et al., Prog. Lipid Res. 36, 153-95, (1997); and Fernandis et al. Curr. Opin. Lipidol. 18: 121-8, (2007)]. The most studied compound was ceramide, and more recently sphingosine phosphate [Hait et al., Biochim. Biophys. Acta, 1758: 2016-26, (2006)]. Ceramide was shown to play a role in the regulation of key processes such as growth inhibition, differentiation and apoptosis [Hannun et al., Biochim. Biophys. Acta 1154, 223-36;, Hannun et al., Trends Cell Biol. 10, 73-80, (2001); Higgins et al., Trends Biochem. Sci. 17, 18-21, (1992); and Yang et al., Cell Biochem. Biophys., 40: 323-50, (2004)].
Sphingomyelin (SPM) is generally considered as the primary metabolic source of ceramide, whose generation in particular locations in the cell makes it suitable for mediating cellular signaling processes. An increased de novo synthesis of ceramide has also been described as a potential source for signaling [Ohanian et al., Cell. Mol. Life Sci., 58: 2053-68, (2001); and Pandey et al., Exp. Mol. Pathol., 82: 298-309, (2007)]. Therefore, a major effort has been directed to modulate the generation of intracellular ceramide by sphingomyelinases, mostly the neutral membrane-bound enzyme, although the acidic enzyme has also been implicated. However, it should be emphasized that modification of the biosynthetic mechanisms such as reduction of the conversion of ceramide to SPM or glycolipids and, in parallel, decreasing its hydrolysis by ceramidases would also increase its concentration in the cell [Dagan et al., Biochim. Biophys. Acta., 1633:161-9, (2003)].
The role of sphingolipids in signal transduction [reviewed in Eyster K. M., Adv. Physiol. Educ., 31: 5-16, (2007); Zheng et al., Biochim. Biophys. Acta, 1758: 1864-84, (2006); Riboni et al., Prog. Lipid Res. 36, 153-95, (1997); and Gomez-Munoz, Biochim. Biophys. Acta 1391, 32-109, (1998)] have been extensively studied, and were proposed to operate through the “sphingomyelin cycle”. According to this hypothesis, binding a particular extracellular ligand to its receptor activates a plasma membrane-bound sphingomyelinase, giving rise to ceramide, which acts as a mediator of the intracellular effects of the ligand. Numerous publications describe and emphasize the role of ceramide in cell killing by apoptosis, as well as its effect on important cellular events such as proliferation, differentiation and reaction to stress conditions. Of particular interest are also reports that short chain, cell-permeable (e.g., C2, or C6) ceramides evoke biological responses that lead to cell killing [Stover et al., J. Pharmacol. Exp. Ther., 307: 468-75, (2003)]. Other studies, using the precursor of ceramide, sphingosine, have shown its effects on the cell growth and viability. Furthermore, sphingosine was shown to inhibit protein kinase C and to increase the intracellular concentration of calcium ions. The phosphorylated form of sphingosine, sphingosine-1-phosphate, has been shown to be a potent activator of phospholipase D; di- or tri-methylated sphingosine was shown to inhibit growth of cancer cells [Endo et al., Cancer Research, 51, 1613-8, (1981)].
WO 03/027058, relates to a group of compounds suitable for the treatment of parasitic diseases and cancerous diseases for killing of wild type and drug-resistant cancer cells, particularly by inhibiting the synthesis of sphingolipids and ceramides. The compounds disclosed in WO 03/027058, essentially have an alkyl backbone substituted with an alkyl or alkenyl chain which itself may be substituted.
It has now surprisingly been found that the compounds of WO 03/027058, are also effective against immuno-degenerative disorders, in particular against GVHD (Graft Versus Host Disease). GVHD is a type of incompatibility reaction of transplanted cells against host tissues that possess an antigen not possessed by the donor. It is a common complication of allogeneic bone marrow transplantation. After bone marrow transplantation, T cells present in the graft, either as contaminants or intentionally introduced into the host, attack the tissues of the transplant recipient after perceiving host tissues as antigenically foreign. A wide range of host antigens can initiate GVHD, among them the HLAs. However, GVHD can occur even when HLA-identical siblings are the donors. HLA-identical siblings or HLA-identical unrelated donors (called a minor mismatch as opposed to differences in the HLA antigens, which constitute a major mismatch) often still have genetically different proteins that can be presented on the MHC.
Clinically, GVHD is divided into acute and chronic forms. The acute or fulminant form of the disease is observed within the first 100, days post-transplant, and the chronic form of GVHD is defined as that which occurs after 100, days. This distinction is not arbitrary: acute and chronic GVHD appear to involve different immune cell subsets, different cytokine profiles, and different types of target organ damage.
Classically, acute GVHD is characterized by selective damage to the liver, skin and mucosa, and the gastrointestinal tract. Newer research indicates that other GVHD target organs include the immune system itself (the hematopoietic system, e.g. the bone marrow and the thymus), and the lungs in the form of idiopathic pneumonitis. Chronic GVHD damages the above organs, but also causes changes to the connective tissue (e.g. of the skin and exocrine glands).
GVHD can largely be avoided by performing a T-cell depleted bone marrow transplant. These types of transplants result in reduced target organ damage and generally less GVHD, but at a cost of diminished graft-versus-tumor effect, a greater risk of engraftment failure, and general immunodeficiency, resulting in a patient more susceptible to viral, bacterial, and fungal infection. Methotrexate and cyclosporin are common drugs used for GVHD prophylaxis. In a multi-center study [Lancet 2005, Aug. 27-Sep. 2; 366, (9487):733-41], disease-free survival at 3, years was not different between T cell depleted and T cell replete transplants.
While donor T-cells are undesirable as effector cells of GVHD, they are valuable for engraftment by preventing the recipient's residual immune system from rejecting the bone marrow graft (host-versus-graft). Additionally, as bone marrow transplantation is frequently used to cure malignant disorders (most prominently the leukemias), donor T-cells have proven to have a valuable graft-versus-tumor effect. A great deal of current research on allogeneic bone marrow transplantation involves attempts to separate the undesirable GVHD aspects of T-cell physiology from the desirable graft-versus-tumor effect.
A key function of the immune system is the control of self-reactivity. Under normal circumstances, the immune system is unresponsive to self-antigens. However, when the immune balance is perturbed, self-reactive lymphocytes may cause autoimmune diseases. Different diseases may develop, depending on the targets of sensitized T cells and antibodies reacting against self-antigens. Thus, lymphocytes reacting against encephalitogenic determinants of the central nervous system typically cause multiple sclerosis (MS), whereas lymphocytes reacting against pancreatic islets typically cause type 1 insulin dependent diabetes mellitus (IDDM). Other autoimmune diseases may be mediated primarily by antibodies such as autoimmune hemolytic anemia, while other autoimmune syndromes may result in multi-organ or systemic disease, such as systemic lupus erythematosus (SLE).
As for the involvement of ceramide and sphingolipid metabolism in cancer, pertinent to this are two lines of study: The first demonstrated that apoptosis induced by administration of a variety of chemotherapeutic agents is mediated by ceramide [Jarvis et al., Curr. Op in. Oncol., 10: 552-9, (1998) ; Kolesnick et al., Oncogene, 22: 5897-906, (2003); Charles et al., Cancer Chemother. Pharmacol., 47: 444-50, (2001); and Hail et al., Apoptosis, 11: 1677-94, (2006)]. Anthracyclins (e.g., daunorubicin) have been shown to induce ceramide accumulation which subsequently led to death of cancer cells [Cuvillier et al., Cell Death Differ., 8: 162-71, (2001)]. The second line of study showed that drug-resistant cancer cells differ in their sphingolipid metabolism from drug-sensitive ones. Of special interest in this respect are the studies of Cabot [Liu et al., FASEB J., 15: 719-30, (2001) and Gouaze et al., Mol. Cancer Ther., 3: 633-9, (2004)] which demonstrate that glucosylceramide, a direct metabolic product of ceramide, is elevated in several drug-resistant cells overexpressing the P-glycoprotein pump (Pgp). Overexpression of glucosylceramide synthetase (GCS), which synthesizes said glycolipid, by a retroviral expression system, results in conversion of doxorubicin-sensitive cells into resistant ones [Liu et al., J. Biol. Chem., 274: 1140-6, (1999)]. Conversely, inhibition of GCS expression, by antisense technology, results in increased sensitivity to doxorubicin. Cabot also suggests that drug-resistance modulators, such as tamoxifen, verapamil, and cyclosporine analog PSC 833, exert their effect by inhibition of GCS [Cabot et al., FEBS Lett. 394, 129-131, (1996); Cabot et al., FEBS Lett. 431, 185-99, (1998); Lavie et al., J. Biol. Chem., 272, 1682-7, (1997); and Lucci et al., Cancer 86, 300-311, (1999)] resulting in an increase of cellular ceramide. Accordingly, Nicholson [Nicholson et al., Br. J. Cancer, 81, 423-30 (1999)] shows that the GCS inhibitor, 1-phenyl-2-decanoylamino-3-morpholine-1-propanol, killed preferentially multidrug-resistant cells, compared to their drug-sensitive counterparts. Taken together, the above studies suggest a metabolic mechanism, which in MDR-cells decreases their ceramide content by converting it to glucosylceramide, making them resistant to a series of chemotherapeutic drugs. As for the relationship between ceramide induction of apoptosis and death to breast cancer, a few recent publications [Scarlatti et al., FASEB J. 71, 2239-2341, (2003); Gewirtz et al., Breast Cancer Res. and Treatinent 62, 223-235, (2000); and Struckhoff et al., J. Pharm. Exp. Ther. 309, 523-532, (2004)] and the review by Reynolds, Mauer and Kolesnick [Reynolds et al., Cancer Letters 206, 169-180, (2004)] summarize the relationship between these three elements and discuss the potential effect of pharmacological manipulation of sphingolipids metabolism to enhance tumor cell ceramide. Interest in the involvement of ceramide in signaling processes is emphasized by the appearance of thousands of articles and hundreds of reviews on this aspect. However, in view of the crucial role of sphingolipids in many pathologies, need is felt for novel sphingolipid analogs for use as therapeutic agents.
No effective therapy exists against any of the autoimmune diseases, nor is the etiology of either one of the above well understood. However, the feasibility to down-regulate anti-self reactivity may provide an option for cure, regardless of the etiology of each particular autoimmune disease.
In the absence of specific treatment for autoimmune diseases, treatment of patients with active disease is based on symptomatic therapy. Self-reactive lymphocytes cause an uncontrolled inflammatory reaction that is propagated by a cascade of secondary responses. Current medications are used either to control this inflammation, or, in more serious cases, to eliminate or control self-reactive lymphocytes using immunosuppressive agents. However, the immunosuppressive treatment is generally not very effective and is certainly not curative. In addition, long-term consumption of immunosuppressive agents (e.g. corticosteroids; cyclophosphamide; imuran, or cyclosporin A) is frequently associated with severe and occasionally fatal outcomes. These may be due to side effects associated with these drugs, or to the consequences of effective immunosuppression, including infections and secondary malignancy. Therefore, the available modalities are far from being satisfactory in treating autoimmune diseases, particularly not progressive and life-threatening ones such as MS, IDDM or SLE.
It is therefore an object of this invention to provide novel compounds which are in particular suitable for treating proliferative disorders.
It is another object of the present invention to provide novel compounds, and combination of compounds, optionally with a further therapeutic agent, which are suitable in treating infections, metabolic disorders, and degenerative diseases.
Other objects and advantages of the present invention will appear as description proceeds.